This invention relates to highway safety devices, more particularly to energy absorption displaceable barriers extending along a roadway to intercept an errant vehicle leaving the roadway and redirect it back onto the roadway.
It has long been common practice to install fixed guardrails extending along the sides of roads particularly at especially hazardous sites where there is a sudden or abrupt drop-off or an immoveable object adjacent the road or a sharp curve in the road. The most widely used construction is a guardrail comprising standard metal W beams attached to fixed posts at spaced intervals along the roadway. While such guard rails are effective in most cases in preventing a vehicle from travelling a hazardous area, they achieve this result at the cost of excessive damage to the vehicle, risk of injury to the occupants, and damage to the guardrail itself which often requires rebuilding. Risk of injury and vehicle damage occur because of the high deceleration rates unavoidably imparted to the vehicle and the occupants by contact with a fixed rigid guardrail structure, since deceleration rates are a function of the distance over which the deceleration occurs.
Deficiencies of the current fixed rigid guardrail structure are compounded by the snagging of the impacting vehicle wheel against the exposed base of a tipped support post resulting in unacceptably abrupt deceleration and consequent damage to the guardrail, to the vehicle and undue risk of injury to the occupants.
Attempts have been made to prevent this wheel or hub snagging with "blockouts" arranged between the post and the rail. This expedient, which adds to the complexity and cost of the rail system, is effective only up to the design impact severity, beyond which the support posts are broken or uprooted and struck by a vehicle wheel, constituting, ipso facto, a failure of the design intent.